Since we have defined all the requests and response types needed by our service, we are now able to proceed by defining the IItemService interface and its implementation. As a first step, we can create a new Services folder in the Catalog.Domain project and proceed by defining the following IItemService interface:

using System.Collections.Generic;
using System.Threading.Tasks;
using Catalog.Domain.Requests.Item;
using Catalog.Domain.Responses;

namespace Catalog.Domain.Services
{
    public interface IItemService
    {
        Task<IEnumerable<ItemResponse>> GetItemsAsync();
        Task<ItemResponse> GetItemAsync(GetItemRequest request);
        Task<ItemResponse> AddItemAsync(AddItemRequest request);
        Task<ItemResponse> EditItemAsync(EditItemRequest request);
        Task<ItemResponse> DeleteItemAsync(DeleteItemRequest request);
    }
}

The preceding definition exposes the methods needed by our application. First of all, we should notice that all the functions return a Task<T> generic type. We can also see that all the methods end with the Async prefix, which suggests that the implementation will be asynchronous.